A radio propagation characteristics estimation system (radio propagation simulator) is used to assist in arrangement of base stations, base units and the like in a wireless communication system and optimization of parameters for the arranged base stations, base units and the like. To highly accurately estimate radio propagation characteristics, it is necessary to accurately grasp positions and shapes of obstacles present around the base stations and base units serving as radio wave transmitting or receiving points and deterministically consider those positions and shapes. For example, if one of the base stations of the wireless communication system is disposed outdoor, electronic map data in which three-dimensional (hereinafter, “3D map data”) shapes of structures around the base station are accurately stored is necessary.
Conventional methods of creating 3D map data are roughly divided into the following two methods. A first method uses photographs, such as air photographs or satellite photographs, of a data creation target taken from the above. In particular, a stereo imaging method of obtaining a 3D shape of each structure serving as the data creation target by using photographs of the structure taken from two different points and using a disparity between the two photographs is often used. Non-Patent Document 1, for example, discloses the stereo imaging method in detail.
According to the first method, the photographs of an upper surface of each structure are taken in a front view direction. Due to this, external shape information on orthographic projection of the upper surface of the structure can be highly accurately obtained. On the other hand, since the structure is photographed almost in a direction perpendicular to a height of the structure, height information is compressed in each photograph. As a result, an influence of quantization error generated when the photographs are digitized or man-made error generated when an operator extracts feature points of the structure increases, thereby deteriorating accuracy of the height information as compared with the external shape. Furthermore, if other structures are closed together around the data creation target structure, an influence such as shielding of the feature points of the creation target structure often causes further deterioration in accuracy.
A second method for creating 3D map data uses photographs taken by an on-vehicle camera. Patent Document 1, for example, discloses a method including taking photographs of each structure from a moving measuring vehicle on which two cameras are mounted and obtaining height information on the structure based on 3D imaging position data and photographic conditions (a horizontal angle and a vertical angle of a camera visual line, a zoom coefficient and the like) at an instance of photographing.
According to the second method, the height information on the structure can be obtained accurately if the structure is along a road on which the moving measurement vehicle can travel. However, if the structure is not along the road and invisible from the road, the height information on the structure cannot be obtained. Moreover, many structures often have such structures as an attached penthouse and a signboard provided on a roof thereof. If such a structure is invisible from the road, data on the structure cannot be obtained. However, if a created 3D map is applied to a car navigation system, a structure invisible from a road or low accuracy of the structure does not pose serious problems since it is important that information on structures visible to a driver on the road is reproduced with high accuracy.
{Citation List}
{Patent Literature}    JP-A-2003-006680
{Non Patent Literature 1}    Mikio TAKAGI and Akihisa SHIMODA, “Handbook for Image Analysis, New Edition”, pp. 1319-1349, University of Tokyo Press, 2004;
{Non Patent Literature 2}    Jun Sato, “Computer Vision-Vision Geometry”, pp. 30-38 and 146-149, Corona Publishing Co., Ltd.